This invention relates to a multiple-stage bio-reaction process.
Bio-reactions, including fermentation, are used for the production of many useful and valuable commercial products, including the production of ethanol or single cell protein. The commercial viability of a large-scale bio-reaction often depends, however, on the organic materials used as starting material or feedstock for the process. If the materials are expensive, such as corn or corn by-products, the profits of the bio-reaction process can be small. The availability of the materials for a feedstock can be uncertain since other potential uses for the materials can affect market price and availability. It has long been a goal to find a process to use low-quality biomass, which tends to be inexpensive and in large supply, as a feedstock for large scale bio-reaction. Such materials tend to be either agricultural wastes or waste products from industrial processes (such as from the food industry). It has also long been a goal to find a process that will fully utilize high-cost, high-quality feedstock materials such as corn. Most current bio-reaction processes utilize only a portion of the readily available carbohydrates, such as starch, and are unable to fully utilize those that are bound as part of the lignocellulose in the form of hemicellulose and cellulose. Because of this, conventional bio-reaction processes can only utilize approximately 60% of the total nutrients in cereal grains such as corn.
The success of a bio-reaction method capable of utilizing inexpensive feedstocks could have large consequences for many important industrial markets, including those for meat production (i.e. the use of bio-reaction products such as single cell protein as animal feed) and for energy (e.g. the production of ethanol as a fuel additive). Conventional methods, however, are inefficient because they involve complex and costly methods for pre-treating the raw feedstock materials, require costly commercially available purified concentrated enzymes, or poorly utilize the feedstock in the bio-reaction process.
A significant practical impediment to the use of various bio-reaction feedstock materials is the need to purify degradative enzymes such as amylases and cellulases used in the pre-treatment of the raw feedstock. Because these enzymes are themselves produced by microbes in an enzyme-production bio-reaction, the volume in which the enzymes are produced is generally large, requiring significant concentration of the enzymes. Furthermore, in order to aid in the recovery of the enzymes, it is often easier to use liquid bio-reaction which, unlike solid-substrate bio-reactions, does not leave solid residuals which would impede the recovery and concentration of the produced enzymes. For enzyme production the prior art has avoided using solid-substrate bio-reactions because of difficulty of purifying enzyme products, even though the same microbes grow better in a solid-substrate bio-reaction.
It should also be noted that the use of certain raw feedstock materials requires acid hydrolysis pre-treatment in order to render the material accessible to degradatory enzymes during the bio-reaction process. For example, before feedstocks with high cellulosic content can be successfully treated with cellulase enzyme complex, the hemicelluloses are acid hydrolyzed to release the cellulose from lignin, and thus open the cellulosic structure to action by the cellulase enzyme complex. The acid is subsequently neutralized prior to bio-reaction.
Because of its low cost, sulfuric acid is typically used for pre-treatment hydrolysis. However, residual high sulfate content subsequent to neutralization inhibits the subsequent bio-reaction. Furthermore, because of its low cost, slaked lime (Ca(OH)2) is often used as the neutralizing agent. The resultant CaSO4 salt precipitates from the pretreatment suspension, and is removed prior to the bulk bio-reaction as a waste product. The need to remove this precipitate adds cost and complexity to the process, without directly improving the product. It would be advantageous to use a method of acid hydrolysis and neutralization that provides acceptable costs, low or zero waste emission, and directly contributes to the value of the resultant bio-reaction product.
The methods of the present invention can be used to overcome the deficiencies of the prior art, and are described herein.
The present invention uses enzymes produced by a first stage bio-reaction without an intermediate step of enzyme purification. These enzymes can be used directly in a second stage bio-reaction to make high effective use of the feedstock. By so doing, the costs and inefficiencies of enzyme concentration and purification are avoided. Furthermore, the benefits of solid substrate bio-reaction for the production of enzymes can be obtained, without the disadvantages that a solid substrate bio-reaction poses in enzyme purification.
The production of animal feed single-cell protein product from bio-reaction feedstocks with high cellulosic content requires acid hydrolysis followed by base neutralization. It is also a teaching of the present invention that acids and bases be used that have value as nutritional supplements. Thus, given that phosphate minerals are often added as a nutritional supplements in cattle feed, and are also beneficial to microbial growth in the second stage bio-reaction, it is advantageous to use phosphoric acid for acid hydrolysis pretreatment of the raw second stage bio-reaction feedstock, so that its continued presence benefits the second stage bio-reaction, and furthermore adds nutritional value to the animal feed product.
Likewise, the use of ammonium ion (e.g. as ammonium hydroxide or anhydrous ammonia) is beneficial to neutralize the phosphate used in the acid hydrolysis since ammonia provides nutritional value both to the microbes used in the second stage bio-reaction, as well as in the final animal feed product, the ammonia serving as non-protein nitrogen supplement.
The benefits and advantages of the present invention will become more apparent in the specification provided below.